1. Field of Invention
The invention relates to reduction gears and more particularly to such a reduction gear having an increased number of meshed teeth.
2. Description of Related Art
One type of a conventional reduction gear is comprised of a plurality of gears of different diameters meshed together so that an output shaft fixed to, for example, the large gear can rotate in low speed at high torque. The other type of a conventional reduction gear is implemented as a planetary gearing.
Conventionally, there is only one tooth of a gear meshed with that of another gear in either type. That means radial load is mainly borne upon the very few meshed teeth in rotation. This has the drawback of reducing a useful life of the gearsets.
One proposal for eliminating the above drawback is increasing diameters of gears and subjecting the gears to hardening treatment. However, it inevitably will increase the size of gearbox and the manufacturing cost. Both are not desired.
There have been numerous suggestions in prior patents for reduction gear. For example, U.S. Pat. No. 6,832,970 discloses a reduction gear for a starter-generator of an internal combustion engine. Thus, continuing improvements in the exploitation of reduction gear are constantly being sought.